air pollution

Air pollution is the contamination of the atmosphere, or the air in a building, by harmful
gases, vapors, aerosols, and dust particles,
resulting principally from human activities but to a lesser extent from
natural processes. Natural pollutants include pollen particles, salt-water
spray, wind-blown dust, and fine debris from volcanic eruptions. Most human-made air pollutants are the products
of combustion – smoke (from burning
wood, coal, and oil in municipal, industrial, and domestic furnaces); carbon
monoxide from automobiles; and oxides
of nitrogen and sulfur dioxide (mainly from burning coal) – though other industrial processes, crop-spraying,
and (in the past) atmospheric nuclear explosions also contribute. Most air
pollution arises in the urban environment, with a large portion of that
coming from road vehicles. See also air
pollution control.